1. Field of the Invention
The present invention relates, in general, to hydrocarbon conversion processes. More particularly, this invention relates to a hydrocarbon conversion process, which employs a catalyst comprising a metal pentafluoride and hydrogen fluoride, wherein the molar ratio of hydrogen fluoride to metal pentafluoride in a stream obtained from recovering minor amounts of metal pentafluoride from the hydrocarbon effluent from said process is maintained at the ratio desired in said process.
2. Description of the Prior Art
The liquid phase strong acid catalyst system comprising (a) a metal pentafluoride selected from the group of tantalum pentafluoride, niobium pentafluoride and mixtures thereof and (b) hydrogen fluoride is known to be useful in promoting various hydrocarbon conversion reactions (see, for example, U.S. Pat. Nos. 2,683,763; 2,683,764; 3,728,411; 3,852,184; 3,888,937; 3,901,790; 3,948,761; as well as application Ser. No. 586,176, filed June 12, 1975, which issued as U.S. Pat. No. 4,025,577 on May 24, 1977, the disclosures of which were incorporated herein by reference). These reactions include isomerization, alkylation, disproportionation, naphthene cleavage, aromatic hydrogenation, and the like.
Generally, in such conversion reactions, the conversion zone effluent is subsequently separated by settling into two phases, namely, a predominantly hydrocarbon phase and a predominantly acid catalyst phase. Although the major portion of the metal pentafluoride that was present in the conversion zone effluent settles in the acid phase, a minor but significant amount of the metal pentafluoride along with some hydrogen fluoride is carried over into the hydrocarbon phase. The concentration of the metal pentafluoride in such hydrocarbon streams typically ranges from about 5 to 10,000 wppm. Although the amount of metal pentafluoride in the hydrocarbon stream may be small, its presence results in numerous difficulties in the process equipment, e.g., fouling and corrosion of the equipment. Furthermore, the loss of these amounts of metal pentafluoride represents a considerable economic disadvantage since fresh metal pentafluoride would have to be added to the system to compensate for that discharged in the hydrocarbon. Thus the recovery of the trace amounts of metal pentafluoride from the hydrocarbon phase for reuse as catalyst would have both economic and process benefits.
One method of recovering the metal pentafluoride is disclosed in U.S. Pat. No. 3,830,870, the disclosures of which are incorporated herein by reference. According to this method, a hydrocarbon stream containing minor amounts of metal pentafluoride is contacted with substantially anhydrous liquid hydrogen fluoride such that there is formed an extract phase containing predominantly hydrogen fluoride and at least a portion of the metal pentafluoride thus removed. Typically, the mole ratio of hydrogen fluoride to metal pentafluoride is more than 100:1. However, it is known that the effectiveness of this catalyst system in hydrocarbon conversion processes is related to the molar ratio of hydrogen fluoride to said metal pentafluoride. More particularly, in order to maximize catalyst activity and activity maintenance, it is desirable to operate said processes at a catalyst composition wherein the molar ratio of HF to metal pentafluoride is at least equal molar, preferably at least 5, more preferably at least 10, but less than 40. Most preferably, the molar ratio is maintained within the range of from 5 to 40.
One method for adjusting the molar ratio of HF to metal pentafluoride in the extract phase is to remove a portion of the hydrogen fluoride by distillation as described in the patent. However, this method requires expenditures for the separate distillation zone. Thus, it would be highly desirable to have available a simple and convenient method of adjusting the molar ratio of hydrogen fluoride to metal pentafluoride in the extract phase to the level desired in hydrocarbon conversion process which does not involve the necessity of additional equipment other than that normally employed in said process.